Process for preparing conductive polymeric particles with linear and crosslinked portions

ABSTRACT

A process for the preparation of conductive polymeric particles with linear and crosslinked portions, which comprises mixing a monomer with at least one conductive filler, solvent, at least one polymerization initiator, and a chain transfer component; effecting solution polymerization by heating until from about 80 to about 100 weight percent of the monomer has been polymerized; drying the mixture by removing the solvent to yield an intimate blend of polymer with conductive filler; dispersing the aforementioned blend of polymer and conductive filler in at least one monomer with at least one polymerization initiator, a crosslinking agent and a chain transfer agent to form an organic phase; dispersing the resulting organic phase mixture in water containing a stabilizing component to obtain a suspension of particles with an average volume diameter of from about 0.05 to about 5 microns in water; polymerizing the resulting suspension by heating; and subsequently optionally washing and drying the polymeric product.

This is a continuation, of application Ser. No. 225,855, filed Apr. 11,1994, now U.S. Pat. No. 5,487,847.

BACKGROUND OF THE INVENTION

This invention is generally directed to conductive composite particlesand processes for the preparation thereof, and more specifically thepresent invention relates to small conductive polymeric compositeparticles, each comprising a polymer and a conductive fillerdistributed, preferably evenly throughout the polymer matrix ofcomposite. The present invention also relates to processes for thepreparation of polymeric composite particles. In one embodiment, theprocess of the present invention comprises the preparation of conductivepolymeric particles containing a conductive filler distributedsubstantially throughout the polymer matrix of the particles, and whichparticles can be selected as carrier powder coatings. In anotherembodiment, the process of the present invention comprises thepreparation of conductive polymeric composite particles with an averagevolume particle size diameter of from between about 0.05 micron to about5 microns. The conductivity of the generated submicron polymericcomposite particles can be modified by, for example, varying the weightpercent of conductive filler component present in effective amounts of,for example, from between about 1 weight percent to about 50 weightpercent, and also by varying the composition of the conductive fillercomponent. Thus, in embodiments conductive submicron polymeric compositeparticles with a conductivity of from between about 10⁻¹⁰ (ohm-cm)⁻¹ toabout 10⁻¹ (ohm-cm)⁻¹ can be prepared. In embodiments, the particleswith average diameter of about 0.05 to about 5 microns conductivecomposite particles are comprised of polymer and a conductive fillerdistributed evenly throughout the polymer matrix of the compositeproduct, and which product can be obtained by a modified semisuspensionpolymerization method in which at least one monomer is mixed with aconductive filler, solvent, one or more polymerization initiators, and achain transfer component; effecting solution polymerization by heatinguntil from about 80 to about 100 weight percent of the monomer has beenpolymerized; drying the mixture by removing the solvent; dispersing theaforementioned mixture of conductive filler or fillers and polymer in atleast one monomer with one or more polymerization initiators, acrosslinking agent and a chain transfer agent; dispersing the resultingmixture in water containing a stabilizing component to obtain asuspension of particles with an average diameter of from about 0.05 toabout 5 microns in water; polymerizing the resulting suspension byheating; and subsequently optionally the product is washed and dried.

Metals such as carrier cores are conductive or semiconductive materials,and the polymeric materials used to coat the surface of metals areusually insulating. Therefore, carrier particles coated completely withpolymer or a mixture of polymers can lose their conductivity and becomeinsulating. Although this is desired for some applications, forconductive magnetic brush systems (CMB) the carrier particles should beconductive. Since the carrier polymer coating can be utilized to controlcarrier tribo, a conductive carrier coating is needed to design carrierswith the desired conductivity and triboelectrical properties. Conductivepolymers are very costly, and are not suitable for preparing low cost,for example less than $5/pound, coating, thus a conductive polymercomposite comprising a low cost polymer and a conductive filler, such asconductive carbon black, is considered a more suitable alternative.

A polymer composite coating of metal materials, such as carrier beads,is known and can generally be obtained by two general approaches,solution and powder coating. Solution coating of carriers with a polymercomposite solution comprised of a polymer, a conductive filler andsolvent can be utilized to prepare conductive carrier, however, trappingof solvent in the solution coating can adversely interfere with the useof coated materials, for example the residual solvent trapped in thecarrier coating reduces the carrier life, and the release of solvent inthe developer housing can cause other problems related to the harmfuleffects of absorbed solvent to various copying machine parts and thetoxicity of solvent. Moreover, the solvent recovery operation involvedin the solution coating processes is costly. The powder coating of metalsurfaces can eliminate the need for solvent, and therefore, many of theproblems associated with solution coating; however, it requires apolymer powder with a very small size, for example less than 1 to 5microns. Although polymer powders are available for carrier powdercoating, submicron or micron-sized polymer composite particlescontaining conductive filler to prepare conductive coated carriers thatmaintain their triboelectrical characteristics for extended time periodsexceeding, for example, 200,000 images and which possess the otheradvantages illustrated herein are desired.

Semisuspension polymerization process is known, reference U.S. Pat. No.5,236,629, the disclosure of which is totally incorporated herein byreference. The '629 patent describes a process for the preparation ofconductive submicron polymeric particles which comprises mixing at leastone monomer with a polymerization initiator, a crosslinking componentand a chain transfer component; effecting bulk polymerization until fromabout 10 to about 50 weight percent of the monomer has been polymerized;terminating polymerization by cooling the partially polymerized monomer;adding thereto from about 1 to about 50 weight percent of a conductivefiller, or conductive fillers, followed by mixing thereof; dispersingthe aforementioned mixture of conductive filler or fillers, andpartially polymerized product in water containing a stabilizingcomponent to obtain a suspension of particles with an average diameterof from about 0.05 to about 1 micron in water; polymerizing theresulting suspension by heating; and subsequently washing and drying theproduct. There are some disadvantages with the '629 process which can beovercome by the modified semisuspension polymerization process of thepresent invention. For example, although most carbon blacks, which areknown to be free radical inhibitors, can be used in the '629 process,those carbon blacks which are very strong inhibitors, for example somehighly oxidized carbon blacks, can inhibit the polymerization of the'629 process. In the modified semisuspension polymerization process ofthe present invention it is possible to select very strongly inhibitingcarbon blacks. Furthermore, the nature of the conductive fillerdispersion in the '629 process is one of free filler particlesphysically dispersed in the polymer matrix, while in the modifiedsemisuspension polymerization process of the present invention thefiller, such as carbon black, contains the polymer made in the solutionpolymerization step chemically grafted or strongly adsorbed onto itssurface thereby enhancing its dispersion stability. Therefore, with thepresent invention there are fewer problems associated with free fillerparticles that can occur in the '629 process if the bulk polymerizationstep is not conducted to the optimum conversion. The modifiedsemisuspension polymerization process of the present invention alsoprovides advantages in obtaining a more uniform dispersion of filler inthe final particles primarily because of the grafted or adsorbed polymeron the filler surface. While some additives are difficult to disperse invarious monomers, depending on the surface compatibility of the fillerand monomers, the modified semisuspension polymerization processovercomes this difficulty by chemically grafting or adsorbing polymer onthe filler surface during the solution polymerization. This solutionpolymerization step, therefore, compatibilizes the filler with themonomer, thereby ensuring better filler dispersion than in the '629process. This results in fewer final particles without filler, which isparticularly important for conductive particles, as there can be asignificant decrease in conductivity when even a small fraction ofnonconductive particles, that is particles without filler, are mixed inwith the conductive particles.

The preparation of polymeric particles for powder coatings can beaccomplished, for example, by three methods, namely grinding orattrition, precipitation and in situ particle polymerization. Grindingor attrition, especially fluid energy milling, of large polymericparticles or polymeric composite particles containing fillers to thesize needed for powder coating, for example less than 1 to 5 microns, isoften not desirable both from an economic and functional viewpoint.These materials are difficult to grind and, therefore, grinding orattrition of required materials for coating with present millingequipment is very costly due to very low processing yield, for examplein the range of 5 to 10 weight percent. Precipitation process can alsobe used to prepare polymeric/polymeric composite particles. In oneprocess, the polymer solution is heated to above its melting temperatureand then cooled to form particles. In another process, the polymersolution is precipitated using a nonsolvent or the polymer solution isspray dried to obtain polymeric/polymeric composite particles. With allthese precipitation processes, it has been difficult to achieve lowcost, pure polymer, that is, for example, with no or substantially noimpurities such as solvents or precipitants in the resulting polymerparticles. It is also difficult to obtain particles with small particlesize and narrow particle size distribution. It is also difficult tocontrol filler distribution throughout each particle's polymer matrix.In the in situ particle polymerization process, polymer particles areprepared by using suspension dispersion, emulsion and semisuspensionpolymerization. Suspension polymerization can be utilized to preparepolymer particles and polymeric composite particles containing, forexample, a conductive filler. However, this process does not, forexample, effectively enable particles with a size of less than 5microns. Although emulsion and dispersion polymerization can be utilizedto prepare polymeric particles of a small size, for example less than 5microns, these processes wherein particle formation is achieved bynucleation and growth do not, it is believed, enable synthesis ofparticles containing fillers such as conductive fillers.

There is disclosed in U.S. Pat. No. 4,908,665 a developing roller ordeveloper carrier comprised of a core shaft, a rubber layer and a resincoating layer on the surface of the rubber containing conductive fillersfor a one component developer. It is indicated in the '665 patent that aconductive developing roller can eliminate variation of the imagecharacteristic due to the absorption of moisture for one componentdevelopment. This patent thus describes a developing roller for onecomponent developer. U.S. Pat. No. 4,590,141 discloses carrier particlesfor two component developer coated with a layer of silicon polymer usingfluidized bed solution coating. U.S. Pat. No. 4,562,136 discloses a twocomponent dry type developer of carrier particles coated with a siliconresin containing a monoazo metal complex charging. The two componentcarriers described in the above two patents are insulating and are notbelieved to be conductive. There is disclosed in U.S. Pat. No. 4,912,005a conductive carrier composition coated with a layer of resin containinga conductive particle by solution coating. Residual solvent trapped inthe aforementioned coated layer adversely effects the maintainability ofcarrier electrical properties for an extended time period.

There is disclosed in U.S. Pat. No. 3,505,434 a process whereinparticles for fluidized bed powder coating are prepared by dispersingthe polymer in a liquid which is heated to above the polymer meltingpoint and stirred causing the polymer particles to form. The particlesare then cooled below their melting point and recovered. However, thisprocess does not, for example, enable particles with a size of below 50microns in average volume diameter.

Also, the suspension polymerization of monomer is known for theformation of polymer/polymeric composite particles generally in a sizerange of about 200 microns and higher. The main advantage of suspensionpolymerization is that the product may easily be recovered, therefore,such a process is considered economical. However, it is very difficultby suspension polymerization to prepare very small particles as themonomer droplets tend to coalesce during the polymerization process,especially in the initial stage of polymerization where the droplets arevery sticky. For example, there is disclosed in U.S. Pat. No. 3,243,419a method of suspension polymerization wherein a suspending agent isgenerated during the suspension polymerization to aid in the coalescenceof the particles. Also disclosed in U.S. Pat. No. 4,071,670 is a methodof suspension polymerization wherein the monomer initiator mixture isdispersed in water containing stabilizer by a high shear homogenizer,followed by polymerization of suspended monomer droplets.

Further, disclosed in U.S. Pat. No. 4,835,084 is a method for preparingpigmented particles wherein high concentration of silica powder is usedin the aqueous phase to prevent coalescence of the particles. There isalso disclosed in U.S. Pat. No. 4,833,060 a process for the preparationof pigmented particles by dissolving polymer in monomer and dispersingin the aqueous phase containing silica powder to prevent coalescence ofthe particles. However, the silica powder used in both U.S. Pat. Nos.-084 and -060 should be removed using KOH which is costly, and residualKOH and silica materials remaining on the surface adversely affects thecharging properties of particles. There is also disclosed in U.S. Pat.No. 3,954,898 a two step polymerization process for the preparation of athermosetting finished powder. However, this process does not enablesynthesis of particles with a size less than about 100 microns.Moreover, this patent does not teach the synthesis of submicronparticles containing conductive fillers.

As a result of a patentability search for U.S. Pat. No. 5,043,404(D/89032), there were located U.S. Pat. No. 4,486,559, which disclosesthe incorporation of a prepolymer into a monomer toner mix followed byemulsion polymerization; and 4,680,200 and 4,702,988, which illustrateemulsion polymerization. It is known that submicron polymeric particlescan be synthesized by emulsion polymerization. However, synthesis ofsubmicron polymeric particles by emulsion polymerization requires a highconcentration of emulsifier which remains in the final product andrenders it humidity sensitive. Therefore, emulsion polymerization doesnot enable preparation of clean submicron polymeric particles which arenot sensitive to humidity. Moreover, in the emulsion polymerizationparticle formation is controlled by diffusion of monomer from monomerdroplet through a water phase into the growing particles. Thismechanism, which is characteristic of emulsion polymerization, does notallow inclusion of conductive fillers in the polymeric particles.Furthermore, it is known that the addition of conductive fillers intoemulsion, dispersion or suspension polymerization systems causes severeinhibition which stops or reduces the rate of polymerizationsignificantly.

Disclosed in the aforementioned U.S. Pat. No. 5,043,404 (D/89032), thedisclosure of which is totally incorporated herein by reference, is asemisuspension polymerization process for the preparation of smallpolymeric particles which are comprised of a mixture of monomer orcomonomers, a polymerization initiator, a crosslinking component and achain transfer component which are bulk polymerized until partialpolymerization is accomplished. The resulting partially polymerizedmonomer or comonomers is dispersed in water containing a stabilizercomponent with, for example, a high shear mixer, then the resultingsuspension polymerized, followed by washing and drying the submicronpolymeric particles. U.S. Pat. No. 5,236,629 discloses a process for thepreparation of conductive submicron polymeric particles which comprisesmixing at least one monomer with a polymerization initiator, acrosslinking component and a chain transfer component; effecting bulkpolymerization until from about 10 to about 50 weight percent of themonomer has been polymerized; terminating polymerization by cooling thepartially polymerized monomer; adding thereto from about 1 to about 50weight percent of a conductive filler, or conductive fillers, followedby mixing thereof; dispersing the aforementioned mixture of conductivefiller or fillers, and partially polymerized product in water containinga stabilizing component to obtain a suspension of particles with anaverage diameter of from about 0.05 to about 1 micron in water;polymerizing the resulting suspension by heating; and subsequentlywashing and drying the product.

The modified semisuspension polymerization process described in thepresent application offers a different process with significantimprovements over the process disclosed in U.S. Pat. No. 5,236,629.These advantages include (1) superior uniformity of the conductivefiller in the final particles because of the solution polymerizationstep in which polymer is grafted or adsorbed onto the surface of thefiller; (2) fewer particles containing no conductive filler due toimproved dispersion; (3) higher conductivity in the final particles atthe same weight percent loading of conductive filler because of thebetter filler dispersion; (4) fewer potential problems with freeconductive filler particles contaminating the final product and causing,for example, problems with contamination in the developer housing whenthe particles are coated on carrier cores; and (5) the ability to usefillers which are very strong free radical polymerization inhibitorssuch as some highly oxidized carbon blacks. With the present invention,a process to obtain conductive submicron or micron-sized polymerparticles of less than about 1 to about 5 microns in average volumediameter as determined by a scanning electron microscope, eachcontaining conductive fillers evenly dispersed in the polymer. Thesepolymeric particles contain from about 1 to about 50 weight percent of aconductive filler, such as carbon black, which is evenly distributedthroughout the polymer matrix. This modified semisuspensionpolymerization process permits the preparation of low cost, clean, anddry submicron conductive polymeric particles that can be selected ascarrier powder coatings.

SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to provide conductivesmall polymeric composite particles and processes thereof with many ofthe advantages illustrated herein.

In another object of the present invention there are provided smallconductive submicron polymeric composites comprised of a polymer and aconductive filler distributed evenly and in embodiments uniformlythroughout the polymer matrix of the composite and process for thepreparation thereof.

In yet another object of the present invention there are provided lowcost, clean and dry conductive small polymeric composite particlescomprised of from about 50 to about 99 weight percent of polymer andfrom about 1 to about 50 weight percent of conductive filler distributedthroughout the polymer matrix of the composite as measured by TEM, andprocesses for the preparation thereof.

Another object of the present invention resides in conductive submicronpolymeric composite particles with a conductivity from about 10⁻¹⁰(ohm-cm)⁻¹ to about 10⁻¹ (ohm-cm)⁻¹ and processes for the preparationthereof.

Another object of the present invention resides in conductive submicronpolymeric composite particles with an average particle diameter size offrom about 0.05 micron to about 5 microns.

In another object of the present invention there are provided conductivesmall polymeric composites which can be selected for two componentcarrier powder coatings, reference U.S. Pat. Nos. 4,937,166 and4,935,326, the disclosures of which are totally incorporated herein byreference, and processes for preparing such carriers; and whereinimproved dispersion of conductive fillers can be achieved in submicronconductive carrier coating polymeric composite particles.

In another object of the present invention there are provided simpleprocesses for the formation of small conductive polymeric particles, andmore specifically from about 1 to about 5 micron size (average volumethroughout) conductive polymeric particles.

Also, in another object of the present invention there are providedsimple and economical processes for the formation of conductivesubmicron polymeric particles that can be selected as carrier coatings,reference U.S. Pat. Nos. 4,937,166 and 4,935,326, the disclosures ofwhich are totally incorporated herein by reference.

Another object of the present invention resides in simple and economicalsemisuspension polymerization processes for the preparation of low cost,clean, and dry small conductive polymeric particles, and morespecifically submicron or micron-size conductive polymeric particlesuseful as carrier powder coatings.

Additionally, in another object of the present invention there areprovided as a result of the enhanced degree of control and flexibilityprocesses for the preparation of polymeric particles containing aconductive filler, or fillers with improved flow and fusing properties;and particles that can be selected for conductive carrier powder coatingwith a triboelectric charge in the range, for example, of from about -40to about +40 microcoulombs per gram as determined by the known FaradayCage process.

These and other objects of the present invention can be accomplished inembodiments by the provision of processes for the preparation of smallconductive polymer particles, each containing a conductive filler orfillers distributed evenly throughout the polymer matrix of particles,referred to herein as modified semisuspension polymerization processesin which at least one monomer is mixed with a carbon black, or a metaloxide like tin oxide, a solvent, one or more polymerization initiators,and a chain transfer component; effecting solution polymerization byheating until from about 80 to about 100 weight percent of the monomerhas been polymerized; drying the mixture by removing the solvent toyield a blend of polymer and conductive filler that contains from about10 percent to about 80 percent filler; and dispersing the aforementionedmixture of conductive filler or fillers and polymer in at least onemonomer with one or more polymerization initiators, a crosslinking agentand a chain transfer agent. The viscosity of the organic phase can inembodiments be an important factor in controlling dispersion of theconductive filler in the particles, and which viscosity can be adjustedby the percentage of polymer in the mixture. Typical viscosities are inthe range of from about 10 centipoises to 100,000 centipoises. Theaforementioned mixture is then dispersed in water containing astabilizing component with, for example, a high shear mixer to permitthe formation of a suspension containing small, less than about 10microns, and more specifically from about submicron to about 5 microns,for example, particles therein, and thereafter, transferring theresulting suspension product to a reactor, followed by polymerizationuntil complete conversion to the polymer product is achieved. Thepolymer product can then be cooled, washed and dried. More specifically,the process of the present invention is comprised of (1) mixing amonomer or comonomers with one or more conductive fillers, solvent,polymerization initiators, and a chain transfer component; (2) effectingsolution polymerization by increasing the temperature of theaforementioned mixture to from about 45° C. to about 120° C. until fromabout 80 to about 100 weight percent of monomer or comonomers has beenpolymerized; (3) drying this mixture by removing the solvent to yield anintimate blend of polymer and conductive filler; (4) dispersing thisblend of polymer and conductive filler in monomer or comonomers with atleast one polymerization initiator, a crosslinking component and a chaintransfer component to provide an organic phase; the molecular weight andconcentration of polymer in this organic phase affects the viscosity ofthe organic phase which is an important factor in controlling theconductive filler distribution in the particles; (5) dispersing theorganic phase in from about 2 to about 5 times its volume of watercontaining from about 1 to about 5 weight percent of a stabilizingcomponent to form a suspension with a particle size diameter of fromabout 0.05 micron to about 5 micron particles containing from about 1 toabout 50 weight percent of a conductive filler, or conductive fillersusing a high shear mixer; (6) transferring the resulting suspension to areactor and polymerizing the suspension by increasing its temperature tofrom about 45° C. to about 120° C. to allow the complete conversion ofmonomer or comonomers to polymer; (7) cooling the product and washingthe product with water and/or an alcohol like methanol; (8) separatingpolymer particles from the water/methanol by means of filtration orcentrifugation; and (9) drying the polymeric particles.

The present invention is directed to the preparation of small conductivepolymeric particles, that is with, for example, an average particlediameter in the range of from about 0.05 micron to about 5 microns, andpreferably from about 0.1 to about 1.0 micron as measured by SEMcontaining 1 to about 50 percent and preferably 10 to 20 percent ofconductive filler distributed throughout the polymer matrix ofparticles, and which polymer particles have a number and weight averagemolecular weight of from between about 3,000 to about 500,000 and frombetween about 5,000 to about 2,000,000, as determined by gel permeationchromatography, respectively, in embodiments.

Further, the process of the present invention is directed to thepreparation of conductive polymeric particles of average diameter offrom about 0.1 micron to about 1.0 micron containing 10 to 20 weightpercent of a conductive filter and 80 to 90 weight percent of apolymeric material. This polymeric material can be comprised of linearand crosslinked portions with a number average molecular weight of thelinear portion being from about 3,000 to about 50,000 and a weightaverage molecular weight of from about 100,000 to about 500,000 and from0.1 to about 25 weight percent of a crosslinked portion, and whichpolymer product is useful for carrier coatings. More specifically, theprocess of the present invention in embodiments is directed to thepreparation of conductive polymeric particles of an average diameter inthe range of between about 0.1 to about 1.0 micron, conductive fillerdistributed evenly throughout the polymer matrix particle as measured byTEM with a linear portion having a number average molecular weight inthe range of from about 3,000 to about 50,000, and a weight averagemolecular weight of from about 100,000 to about 500,000 and from about0.1 to about 25 weight percent of a crosslinked portion. This process isas indicated herein and specifically comprises (1) mixing a monomer orcomonomers with a conductive filler with the ratio of monomer orcomonomers to conductive filler being from about 10/1 to about 1/10, asolvent with the ratio of monomer or comonomers to solvent being fromabout 20/1 to about 1/20, at least one polymerization initiator with theratio of monomer or comonomers to initiator being from about 100/2 toabout 100/20, and a chain transfer component with the ratio of monomeror comonomers to the chain transfer component being from about 100/0.01to about 100/1; (2) effecting solution polymerization by increasing thetemperature of the mixture to from about 45° C. to about 120° C. untilfrom about 80 to about 100 weight percent of monomer or comonomers hasbeen converted to polymer with a number average molecular weight of fromabout 3,000 to about 50,000 and a weight average molecular weight offrom about 5,000 to about 40,000, (3) drying this mixture by removingsolvent; (4) dispersing this polymer/filler blend in monomer or monomerswith the ratio of polymer/filler blend to monomers being from about5/100 to about 100/100 with at least one polymerization initiator withthe ratio of monomer or comonomers to initiator being from about 100/2to about 100/20, a crosslinking component with the ratio of monomer orcomonomers to the crosslinking component being from about 100/0.01 toabout 100/5, and a chain transfer component with the ratio of monomer orcomonomers to the chain transfer component being from about 100/0.01 toabout 100/1 to yield an organic phase; (5) dispersing the resultingorganic phase from about 2 to about 5 times its volume in watercontaining from about 1 to about 5 weight percent of a stabilizingcomponent, preferably polyvinylalcohol having a weight average molecularweight of from about 1,000 to about 10,000 to form a suspensioncontaining particles with a particle size diameter of from 0.1 to about1.0 micron by using high shear mixer; (4) transferring the resultingsuspension to a reactor and polymerizing the suspension by increasingits temperature to from about 45° C. to about 120° C. to allow thecomplete conversion of monomer or comonomers to polymer; (5) washing theresulting product with equal volumes of methanol and/or water from about3 to about 5 times; (6) separating polymeric particles fromwater/methanol by means of filtration or centrifugation; and (7) dryingof the polymeric particles. Optionally, the drying step (3) above can beeliminated and the solvent can be removed by an appropriate techniqueafter the monomers have been added as in step (4).

In embodiments, the present invention is directed to a process for thepreparation of conductive small polymeric particles which comprisesmixing at least one monomer with a carbon black, solvent, one or morepolymerization initiators, and a chain transfer component; effectingsolution polymerization by heating until from about 80 to about 100weight percent of the monomer has been polymerized; drying the mixtureby removing the solvent; dispersing the aforementioned mixture ofconductive filler or fillers and polymer in at least one monomer withone or more polymerization initiators, a crosslinking agent and a chaintransfer agent; dispersing this mixture in water containing astabilizing component to obtain a suspension of particles with anaverage diameter of from about 0.05 to about 5 microns in water;polymerizing the resulting suspension by heating; and subsequentlywashing and drying the product.

Illustrative examples of monomer or comonomers present in an amount of,for example, from about 80 to about 99 weight percent, and morepreferably from about 80 to about 90 weight percent include vinylmonomers comprised of styrene and its derivatives such as styrene,α-methylstyrene, p-chlorostyrene and the like; monocarboxylic acids andtheir derivatives such as acrylic acid, methyl acrylate, ethyl acrylate,butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate,methacrylic acids, methyl methacrylate, ethyl methacrylate, butylmethacrylate, octyl methacrylate, acrylonitrile and acrylamide;dicarboxylic acids having a double bond and their derivatives such asmaleic acid, monobutyl maleate, dibutylmaleate; vinyl esters such asvinyl chloride, vinyl acetate and vinyl benzoate; vinyl ketones such asvinyl methyl ketone and vinyl ether ketone; and vinyl ethyl ether andvinyl isobutyl ether; vinyl naphthalene; unsaturated mono-olefins suchas isobutylene and the like; vinylidene halides such as vinylidenechloride and the like; N-vinyl compounds such as N-vinyl pyrrole andfluorinated monomers such as pentafluoro styrene, allylpentafluorobenzene and the like; and mixtures thereof.

Illustrative examples of polymerization initiators present in an amountof, for example, from about 0.1 to about 20 weight percent of monomer,and more preferably from about 1 to about 5 weight percent include azocompounds such as 2,2'azodimethylvaleronitrile, 2,2'azoisobutyronitrile,azobiscyclohexanenitrile, 2-methylbutyronitrile and the like, andperoxide such as benzoyl peroxide, lauryl peroxide,1-1-(t-butylperoxy)-3,3,5-trimethylcyclohexane,n-butyl-4,4-di-(t-butylperoxy)valerate, dicumyl peroxide and the like.

Crosslinkers selected for the process of the present invention are knownand can be comprised of compounds having two or more polymerizabledouble bonds. Examples of such compounds include aromatic divinylcompounds such as divinylbenzene and divinylnaphthalene; carboxylic acidesters having two double bounds such as ethylene glycol diacrylate,ethylene glycol dimethylacrylate and the like; and divinyl compoundssuch as divinyl ether, divinyl sulfite, divinyl sulfone and the like.Among these, divinylbenzene is particularly useful. The crosslinkingcomponent is preferably present in an amount of from about 0.1 to about5 parts by weight in 100 parts and, more preferably, from 0.2 to 1 partby weight of the monomer or comonomers.

Examples of conductive fillers present in effective amounts, forexample, from about 1 to 50 weight percent and more preferably from 5 to30 weight percent, and the like, and which amounts can in embodiments bebased on (1) how much filler is needed for minimum effect onconductivity, and (2) achieving a conductivity plateau includingconductive carbon blacks such as acetylene black, available from ChevronChemical, VULCAN BLACK™, BLACK PEARL L®, KETJENBLACK EC600JD®, availablefrom AKZ0, CONDUCTEX SC ULTRA™, available from Columbian Chemical, metaloxides such as iron oxides, TiO, SnO₂, metal powders such as ironpowder, and the like.

Stabilizers present in an amount of, for example, from about 0.1 toabout 5 weight percent and, more preferably, from 1 to 4 weight percentof water are selected from the group consisting of both nonionic andionic water soluble polymeric stabilizers such as methyl cellulose,ethyl cellulose, hydroxypropyl cellulose, block copolymer such asPLURONIC E87™ available from BASF, the sodium salt of carboxyl methylcellulose, polyacrylate acids and their salts, polyvinyl alcohol,gelatins, starches, gums, alginates, zein, casein and the like; andbarrier stabilizers such as tricalcium phosphate, talc, barium sulfateand the like. Polyvinyl alcohol with a weight average molecular weightof from about 1,000 to about 10,000 is particularly useful.

Chain transfer components selected, which primarily function to controlmolecular weight by inhibiting chain growth, include mercaptans such aslaurylmercaptan, butylmercaptan and the like, or halogenated carbonssuch as carbon tetrachloride or carbon tetrabromide, and the like. Thechain transfer agent is preferably present in an amount of from about0.01 to about 1 weight percent and more preferably from 0.1 to 0.5weight percent monomer or comonomers. Also, stabilizer present on thesurface of the polymeric particles can be washed using an alcohol suchas, for example, methanol and the like, or water. Separation of washedparticles from solution can be achieved by any classical separationtechnique such as filtration, centrifugation and the like. Classicaldrying techniques such as vacuum drying, freeze drying, spray drying,fluid bed drying and the like can be selected for drying of thepolymeric particles.

Illustrative specific examples of polymer or copolymers present in anamount of about 50 to about 99 weight percent, more preferably from 70to 95 weight percent., and from about 5 to about 300 percent inembodiments containing, for example, both a linear and a crosslinkedportion in which the ratio of crosslinked portion to linear portion isfrom about 0.001 to about 0.25 and the number and weight averagemolecular weight of the linear portion is from about 3000 to about500,000 and from about 5,000 to about 2,000,000, respectively, includevinyl polymers of polystyrene and its copolymers, polymethylmethacrylateand its copolymers, unsaturated polymers or copolymers such asstyrene-butadiene copolymers, fluorinated polymers or copolymers such aspolypentafluorostyrene, polyallylpentafluorobenzene and the like.

The particles of the present invention can be selected as carrier powdercoatings, which carriers contain, for example, a steel core, and can beadmixed with toner compositions comprised of resin particles, pigmentparticles and optional additives such as charge control components,reference U.S. Pat. No. 4,560,635, the disclosure of which is totallyincorporated herein by reference, enabling the formation of a developercomposition useful in electrophotographic imaging and printingprocesses.

The following Examples are being submitted to further define variousspecies of the present invention. These Examples are intended to beillustrative only and are not intended to limit the scope of the presentinvention. Also, parts and percentages are by weight unless otherwiseindicated.

EXAMPLE I

In a 1 liter glass reactor 150 grams of REGAL 330®carbon black wereadded to 500 grams of toluene with 5 grams of2'-azobis(2,4-dimethylvaleronitrile), 2 grams of benzoyl peroxide, 5grams of dodecanethiol (chain transfer agent) and 150 grams of methylmethacrylate monomer. The resulting mixture was polymerized at 50° C.for 24 hours. The temperature was then increased to 70° C. for 3 hoursto complete the polymerization. The resulting product was vacuum dried.176 Grams of this solution polymerized blend of PMMA(polymethylmethacrylate) and carbon black (CB) were dispersed in 510grams of methyl methacrylate monomer for 48 hours, and then 40 grams of2,2'-azobis(2,4-dimethylvaleronitrile), 16.0 grams of benzoyl peroxideand 3.0 grams of divinylbenzene crosslinking agent were added, and mixeduntil dispersed. This monomer/polymer/CB phase was then mixed with 2,200milliliters of water containing four weight percent of polyvinyl alcohol(weight average molecular weight 3,000) and vigorously stirred at 10,000rpm for 5 minutes to produce a microsuspension of polymeric particles inwater. The suspension polymerization temperature was raised to 60° C.for 2 hours, and then to 85° C. for 1 hour. The microsuspension productwas washed in 5 liters of methanol. A second wash was accomplished withmethanol/water (50:50 ratio) and a third wash with deionized water.After the final wash, the product was freeze dried. Using a scanningelectron microscope (SEM), photomicrographs of the dry product showedthe average particle size of the polymer product was 0.8 micron with aglass transition temperature of 113° C. as measured by DSC. Evaluationshowed the powder product conductivity was 10⁻² (ohm-cm)⁻¹, asdetermined by measuring the electrical resistance of a pressed powderpellet, Transmission Electron Microscopy showed less than 1 percentunpigmented partiicles. 0.7 Gram of the resulting polymethylmethacrylate particles containing carbon black were mixed with 100 gramsof Hoeganoes core carrier with an average bead diameter of 90 microns ina Munson type mixer at room temperature. The coated materials were thenfused on the surface of the carrier at 350° F. in a rotary kiln furnace.The product was sieved through a 177 micron screen to remove coarsematerials. The coarse fraction was found to be about 0.08 weightpercent. The sieved materials were scanned for surface coverage usingthe SEM. The results evidenced 100 percent surface coverage of polymer.A functional evaluation of the resulting carrier in the XeroxCorporation 5100 two component development system indicated it had atriboelectric charge (tribo) of 26 microcoulombs per gram (μc/g) and aconductivity of 10⁻⁸ (ohm-cm)⁻¹ as determined by the Faraday Cagemethod. Thermal gravimetric analysis evidenced that the carbon blackcontent was 12.7 weight percent, indicating all the carbon blackremained in the interior of the particles, and that there was no freecarbon black.

EXAMPLE II

The process of Example I was repeated except that styrene monomer wasused instead of methyl methacrylate. The resulting product has anaverage particle size of 0.7 micron with a conductivity of 10⁻³(ohm-cm)⁻¹ and glass transition temperature of 102° C. The same carriercoating as described in Example I was used resulting in a 0.6 weightpercent coarse fraction. The coated carrier had a tribo of 15microcoulombs per gram and a conductivity of 10⁻⁸ (ohm-cm)⁻¹.

EXAMPLE III

The process of Example I was repeated except that 150 grams of CONDUCTEX975™ carbon black were used. The resulting polymeric product had anaverage particle size diameter of 0.7 micron and a glass transitiontemperature of 115° C. The same carrier coating as described in ExampleI was used resulting in a coarse fraction of 0.5 weight percent. Thecoated carrier had a tribo charge of 28 microcoulombs per gram and aconductivity of 10⁻⁸ (ohm-cm)⁻¹ as determined by the Faraday Cagemethod.

EXAMPLE IV

The process of Example I was repeated except 50 grams of acetylene black(Chevron Shawinigan Company) were used. The resulting polymeric producthad an average particle size of 0.6 micron with glass transitiontemperature of 111° C. The same carrier coating process as described inExample I was used resulting in a coarse fraction of 0.3 weight percent.The coated carrier had a tribo charge of 31 microcoulombs per gram and aconductivity of 10⁻¹⁰ (ohm-cm)⁻¹.

EXAMPLE V

The process of Example I was repeated except that pentafluorostyrenemonomer was used. The resulting product had an average particle size of0.9 micron and glass transition temperature of 106° C. The same carriercoating as described in Example I was used resulting in a 0.2 weightpercent coarse fraction. The coated carrier had a tribo charge of -25microcoulombs per gram.

COMPARATIVE EXAMPLE 1

An experiment analogous to Example I was conducted using the processdisclosed in U.S. Pat. No. 5,236,629. REGAL 330®carbon black (82 grams)was dispersed in 510 grams of methyl methacrylate monomer with 40 gramsof 2,2'-azobis(2,4-dimethylvaleronitrile), 16.0 grams of benzoylperoxide and 3.0 grams of divinylbenzene crosslinking agent. Thisorganic phase was partially bulk polymerized by heating to 45° C. until12 weight percent of the monomer had been converted to polymer, and thencooled to 10° C. The resulting mixture was then mixed with 2,200milliliters of water containing four weight percent polyvinyl alcohol(molecular weight M_(w) 3,000) and vigorously stirred at 10,000 rpm for5 minutes. The suspension polymerization temperature was raised to 60°C. for 2 hours, and then to 85° C. for 1 hour. The microsuspensionproduct was washed and dried as in Example I. SEM photomicrographs ofthe dry product showed the average particle size diameter of the polymerproduct was 0.9 micron. Evaluation showed the powder conductivity was10⁻³ (ohm-cm)⁻¹, compared to 10⁻² (ohm-cm)⁻¹ for Example I as determinedby measuring the electrical resistance of a pressed powder pellet.Transmission electron microscopy showed approximately 3 to 4 percent ofunpigmented particles, compared to less than 1 percent for Example I.0.7 Gram of the resulting polymethyl methacrylate particles containingcarbon black were mixed with 100 grams of Hoeganoes core carrier with anaverage bead diameter of 90 microns in a Munson type mixer at roomtemperature. The coated materials were then fused on the surface of thecarrier at 350° F. in a rotary kiln furnace. The functional evaluationof the resulting carrier in the Xerox Corporation 5100 two componentdevelopment system indicated a triboelectric charge (tribo) of 28microcoulombs per gram (μc/gram), compared to 26 μc/gram for Example I,and a conductivity of 10⁻⁹ (ohm-cm)⁻¹, as compared to 10⁻⁸ (ohm-cm)-1for Example I. Thermal gravimetric analysis evidenced that the carbonblack content was 12.6 weight percent. The modified semisuspensionpolymerization process of the present invention produced more conductivepolymer particles and more conductive carrier than the '629 process.

Conductivity and tribocharge were measured as indicated herein, seeComparative Example 2 for example.

COMPARATIVE EXAMPLE 2

Comparative Example 1 was repeated except that the bulk polymerizationwas stopped when only 6 weight percent of the monomer had been convertedto polymer. SEM photomicrographs of the dry product showed the averageparticle size of the polymer product was 0.5 micron. Evaluation showedthe powder conductivity was 10⁻⁶ (ohm-cm)⁻¹, compared to 10⁻² (ohm-cm)⁻¹for Example I as determined by measuring the electrical resistance of apressed powder pellet. Transmission electron microscopy showedapproximately 10 to 15 percent of unpigmented particles, compared toless than 1 percent for Example I. 0.7 Gram of the resulting polymethylmethacrylate particles containing carbon black were mixed with 100 gramsof Hoeganoes core carrier with an average bead diameter of 90 microns ina Munson type mixer at room temperature. The coated materials were thenfused on the surface of the carrier at 350° F. in a rotary kiln furnace.The functional evaluation of the resulting carrier in the XeroxCorporation 5100 two component development system indicated atriboelectric charge (tribo) of 29 microcoulombs per gram (μc/gram),compared to 26 μc/gram for Example I, and a conductivity of 10⁻¹³(ohm-cm)⁻¹, as compared to 10⁻⁸ (ohm-cm)⁻¹ for Example I. Thermalgravimetric analysis evidenced that the carbon black content was 6.9weight percent compared to 12.7 percent in Example I signifying thatduring the suspension polymerization step free carbon black diffused outof the polymerizing particles into the aqueous phase. This explanationis further evidenced by the observation that large amounts of freecarbon black were observed in the supernatant during the washing of theparticles. This Example indicates that the modified semisuspensionpolymerization process of the present invention is more robust than the'629 process, and that product conductivity can decrease significantly,for example by from about 1 to about 5 orders of magnitude.

Other modifications of the present invention may occur to those skilledin the art subsequent to a review of the present application. Theaforementioned modifications, including equivalents thereof, areintended to be included within the scope of the present invention.

What is claimed is:
 1. A process for the preparation of conductivepolymeric particles with linear and crosslinked portions, whichcomprises in the following order mixing a comonomer with at least oneconductive filler, solvent, at least one polymerization initiator in theamount of about 0.1 to about 20 weight percent of said comonomer, and achain transfer component in the amount of about 0.01 to about 1 weightpercent of said comonomer; effecting solution polymerization by heatinguntil from about 80 to about 100 weight percent of the comonomer hasbeen polymerized; drying the mixture by removing the solvent to yield anintimate blend of polymer with conductive filler; dispersing theaforementioned blend of polymer and conductive filler in at least oneadditional comonomer with at least one polymerization initiator, acrosslinking agent in the amount of about 0.1 to about 5 weight percentof said additional comonomer and a chain transfer agent to form anorganic phase; dispersing the resulting organic phase mixture in watercontaining a stabilizing component in the amount of about 0.1 to about 5weight percent of said water to obtain a suspension of particles with anaverage volume diameter of from about 0.05 to about 5 microns in water;polymerizing the resulting suspension by heating; and subsequentlyoptionally washing and drying the polymeric product to produceconductive polymeric particles wherein the total amount of conductivefiller is from about 1 to about 50 weight percent and the total amountof polymer is from about 50 to about 99 weight percent.
 2. A process inaccordance with claim 1 wherein said comonomer or said additionalcomonomer is a mixture of monomers.
 3. A process in accordance withclaim 2 wherein the mixture contains from 2 monomers to about 20monomers.
 4. A process in accordance with claim 1 wherein thepolymerized polymer product obtained is subjected to continuous washingand drying.
 5. A process for the preparation of conductive polymericparticles with linear and crosslinked portions consisting essentially ofmixing a comonomer with at least one conductive filler, solvent, atleast one polymerization initiator in the amount of about 0.1 to about20 weight percent of said comonomer, and a chain transfer component inthe amount of about 0.01 to about 1 weight percent of said comonomer;effecting solution polymerization by heating until from about 80 toabout 100 weight percent of the comonomer has been polymerized; dryingthe mixture by removing the solvent to yield an intimate blend ofpolymer with conductive filler; dispersing the aforementioned blend ofpolymer and conductive filler in at least one additional comonomer withat least one polymerization initiator, a crosslinking agent in theamount of about 0.1 to 5 weight percent of said additional comonomer anda chain transfer agent to form an organic phase; dispersing theresulting organic phase mixture in water containing a stabilizingcomponent in the amount of about 0.1 to about 5 weight percent of saidwater to obtain a suspension of particles with an average volumediameter of from about 0.05 to about 5 microns in water; polymerizingthe resulting suspension by heating; and subsequently optionally washingand drying the polymeric product to produce conductive polymericparticles wherein the total amount of conductive filler is from about 1to about 50 weight percent and the total amount of polymer is from about50 to about 99 weight percent.
 6. A process in accordance with claim 1wherein heating is accomplished at a temperature of from about 30° C. toabout 200° C.
 7. A process in accordance with claim 1 wherein heating isaccomplished at a temperature of from about 45° C. to about 120° C.
 8. Aprocess in accordance with claim 1 wherein the number average molecularweight of the solution polymerization product is between about 3,000 toabout 500,000, and the weight average molecular weight of the solutionpolymerization product is between about 5,000 to about 2,000,000.
 9. Aprocess in accordance with claim 2 wherein the mixing of the conductivefillers in the mixture of monomers and solvent prior to the solutionpolymerization is achieved with a high shear mixer.
 10. A process inaccordance with claim 1 wherein the dispersion of the mixture ofconductive filler polymer and comonomer or additional comonomer in watercontaining the stabilizing component is accomplished with a high shearmixer.
 11. A process in accordance with claim 1 wherein the ratio of thecrosslinked polymer/linear polymer in the final product is from about0.001 to about 0.25.
 12. A process in accordance with claim 1 whereinthe conductive polymeric particles obtained have an average volumeparticle diameter of from about 0.05 micron to about 5 microns.
 13. Aprocess in accordance with claim 2 wherein the weight percentage ofconductive filler in the final product is from about 1 to about
 50. 14.A process in accordance with claim 1 wherein the conductive filler isevenly distributed throughout the polymer matrix of the final product.15. A process in accordance with claim 1 wherein the conductivity of thefinal conductive polymer product is from about 10⁻¹⁰ to about 10⁻¹(ohm-cm)⁻¹ as determined by measuring the electrical resistivity of apressed pellet.
 16. A process in accordance with claim 1 wherein thenumber and weight average molecular weight of the linear portion of thepolymer in the product polymer is between about 5,000 to about 500,000.17. A process in accordance with claim 1 wherein the triboelectricalcharge of the polymer product is from about +40 to about -40microcoulombs per gram.
 18. A process in accordance with claim 1 whereinthe comonomer or additional comonomer is selected from the groupconsisting of α-methylstyrene, p-chlorostyrene, monocarboxylic acids andthe derivatives thereof; dicarboxylic acids with a double bond and theirderivatives; vinyl ketones; vinyl naphthalene; unsaturated mono-olefins;vinylidene halides; N-vinyl compounds; fluorinated vinyl compounds andmixtures thereof.
 19. A process in accordance with claim 1 wherein thecomonomer or additional comonomer is selected from the group consistingof acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate,dodecyl acrylate, octyl acrylate, phenyl acrylate, methacrylic acids,methyl methacrylate, ethyl methacrylate, butyl methacrylate, octylmethacrylate, acrylonitrile and acrylamide; maleic acid, monobutylmaleate, dibutyl maleate; vinyl chloride, vinyl acetate, vinyl benzoate;vinylidene chloride; pentafluoro styrene allyl pentafluorobenzene andN-vinyl pyrrole.
 20. A process in accordance with claim 1 wherein thefiller is selected from the group consisting of conductive carbonblacks, metal oxides, metals, and mixtures thereof.
 21. A process inaccordance with claim 1 wherein the filler is selected from the groupconsisting of acetylene black, iron oxides, titanium oxide, SnO₂, andiron powder.
 22. A process in accordance with claim 1 wherein thepolymerization initiator is selected from the group consisting of azocompounds and peroxides.
 23. A process in accordance with claim 22wherein the polymerization initiator is benzoyl peroxide, lauroylperoxide, 1-1-(t-butylperoxy)-3,3,5-trimethylcyclohexane,n-butyl-4,4-di-(t-butylperoxy)valerate, dicumyl peroxide,2,2'azodimethylvaleronitrile, 2,2'azoisobutyronitrile,azobiscyclohexanenitrile, or 2-methylbutyronitrile.
 24. A process inaccordance with claim 1 wherein the stabilizing component is selectedfrom a group consisting of nonionic and ionic water soluble polymericstabilizers.
 25. A process in accordance with claim 1 wherein thestabilizing component is selected from the group consisting of methylcellulose, ethyl cellulose, hydroxypropyl cellulose, the sodium salt ofcarboxyl methyl cellulose, polyacrylate acids, polyvinyl alcohol,gelatins, starches, gums, alginates, zein and casein.
 26. A process inaccordance with claim 1 wherein the stabilizing component is tricalciumphosphate, talc or barium sulfate.
 27. A process in accordance withclaim 1 wherein the crosslinking component is selected from the groupconsisting of compounds having two or more polymerizable double bonds.28. A process in accordance with claim 1 wherein the crosslinkingcomponent is divinylbenzene, divinylnaphthalene, ethylene glycoldiacrylate, or divinylether.
 29. A process in accordance with claim 1wherein the chain transfer component is selected from the groupconsisting of mercaptans and halogenated hydrocarbons.
 30. A process inaccordance with claim 29 wherein the chain transfer component is carbontetrachloride, butylmercaptan, or laurylmercaptan.
 31. A process inaccordance with claim 1 wherein from about 0.1 to about 25 of saidpolymeric particles are comprised of crosslinked portions.
 32. A processin accordance with claim 31 wherein from about 1 to about 5 percent byweight of said polymeric particles are comprised of crosslinkedportions.
 33. A process n accordance with claim 1 wherein saidpolymerization initiator is benzoyl peroxide.